1. Field of the Invention
This invention relates to stator structure provided chiefly within the torque converter of an automatic transmission which is employed in controlling the transmission of the driving force of a vehicle.
2. Description of the Related Art
As this kind of conventional stator structure, one employed in the torque converter 2 of an automatic transmission 1, such as that shown in FIGS. 15 through 19, is known.
Within such a torque converter 2, as shown in FIG. 15, a turbine runner 4 is provided and firmly attached to a turbine hub 3 provided so that it is free to rotate.
In this torque converter 2, a pump impeller 5 is provided in opposition to this turbine runner 4 and is firmly attached to a drive sleeve 6.
And between the turbine runner 4 and the drive sleeve 6, there is interposed a stator 8 provided with a plurality of circumferential vane portions 7.
This stator 8 is axially supported on the input shaft of the automatic transmission through a one-way clutch 9, and the front and rear end surfaces of the proximal portion 12 of the stator are contacted with the turbine hub 3 and the drive sleeve 6 through thrust bearings 10 and 11, whereby the stator 8 is allowed to rotate only in one direction and supported so that it is rotatable.
The vane portion 7 of this stator 8, as shown in FIG. 17, is constituted so that the sectional configuration presents a streamline shape, in order to increase a torque which is input to this automatic transmission 1 by employing reaction force which is produced when the flow of oil within the torque converter 2 is abutted in a stall state.
That is, as schematically shown in FIG. 18, with rotation of the pump impeller 5, the turbine runner 4 is given turning force by an oil flow a coming into this turbine runner 4.
And an oil flow b going out from this turbine runner 4 is inverted in a stall state (in which revolution speed of pump impeller 5&gt;&gt;revolution speed of turbine runner 4) by the vane portions 7 of the stator 8 and forms a flow c which joins the flow a.
For this reason, if the torque of the pump impeller 5 is taken to be T1, the transmission torque to the turbine runner 4 to be T2, and the reaction force of the stator 8 to be T3, T2 becomes T1+T3 (i.e., T2=T1+T3). Therefore, the reaction force produced by the flow b abutting on the vane portions 7 is employed, and the torque T2 which is input to the automatic transmission 1 is increased.
Also, if the revolution speed of the turbine runner 4 reaches more than a predetermined value, the direction of the oil flow a going out from the turbine runner 4 will be varied gradually and hit on the back surface side 7a of the vane portion 7.
At this time, the stator 8 is constituted so that it races by operation of the one-way clutch 9 and does not disturb the oil flow b.
Therefore, in the fluid coupling area (where revolution speed of pump impeller 5 is substantially equal to revolution speed of turbine runner 4), oil flows smoothly along the configuration of the vane portions 7.
In Japanese Utility Model Publication No. B7-44,841, there is described a stator 8 with large and small vane portions 7 alternately provided so that flow disturbance due to the revolution speed can be rectified.
In such conventional stator structure, there is known a method which thins the sectional configuration of the vane portion 7 to increase the oil passage area between the vane portions 7 and 7, in order to transmit driving force efficiently to the output side by making the coupling point of the torque converter 2 a higher speed ratio to suppress slippage as much as possible.
However, if the vane portion 7 is thus thinned, the torque capacity will increase and therefore loss of heat in the stall state will increase.
Hence, as shown by the alternate long and two short dashed line in FIG. 19, the point edge 7b near the inlet of the vane portion is curved downward, and a tuning operation for separating an oil flow d purposely at the back surface side of the upper inlet portion is performed.
However, the problem is that the oil separated from the back surface side 7e of the upper inlet portion by such a tuning operation will be vortical and will increase fluid sound along with separated vortexes of oil also arising at the back surface side near the exit 7c.